Controllable fallback (#40)

Add configuration variable `NUMBA_DPPY_FALLBACK_ON_CPU`

Author: 1e-to

numba_dppy/config.py

@@ -34,3 +34,5 @@ def _readenv(): ...
 
 # Turn SPIRV-VALIDATION ON/OFF switch
 SPIRV_VAL = _readenv("NUMBA_DPPY_SPIRV_VAL", int, 0)
+
+FALLBACK_ON_CPU = _readenv("NUMBA_DPPY_FALLBACK_ON_CPU", int, 1)

numba_dppy/dppy_lowerer.py

@@ -1171,7 +1171,8 @@ def lower(self):
             if numba_dppy.compiler.DEBUG:
                 print("Failed to lower parfor on DPPY-device. Due to:\n", e)
             lowering.lower_extensions[parfor.Parfor].pop()
-            if (lowering.lower_extensions[parfor.Parfor][-1] == numba.parfors.parfor_lowering._lower_parfor_parallel):
+            if ((lowering.lower_extensions[parfor.Parfor][-1] == numba.parfors.parfor_lowering._lower_parfor_parallel) and
+                numba_dppy.config.FALLBACK_ON_CPU == 1):
                 self.cpu_lower.lower()
                 self.base_lower = self.cpu_lower
             else:

numba_dppy/tests/test_controllable_fallback.py

@@ -0,0 +1,72 @@
+import numpy as np
+
+import numba
+import numba_dppy
+from numba_dppy.testing import unittest
+from numba_dppy.testing import DPPYTestCase
+from numba.tests.support import captured_stderr
+import dpctl
+
+
+@unittest.skipUnless(dpctl.has_gpu_queues(), 'test only on GPU system')
+class TestDPPYFallback(DPPYTestCase):
+    def test_dppy_fallback_true(self):
+        @numba.jit
+        def fill_value(i):
+            return i
+
+        def inner_call_fallback():
+            x = 10
+            a = np.empty(shape=x, dtype=np.float32)
+
+            for i in numba.prange(x):
+                a[i] = fill_value(i)
+
+            return a
+
+        numba_dppy.compiler.DEBUG = 1
+        with captured_stderr() as msg_fallback_true:
+            with dpctl.device_context("opencl:gpu") as gpu_queue:
+                dppy = numba.njit(parallel=True)(inner_call_fallback)
+                dppy_fallback_true = dppy()
+
+        ref_result = inner_call_fallback()
+        numba_dppy.compiler.DEBUG = 0
+
+        np.testing.assert_array_equal(dppy_fallback_true, ref_result)
+        self.assertTrue('Failed to lower parfor on DPPY-device' in msg_fallback_true.getvalue())
+
+    @unittest.expectedFailure
+    def test_dppy_fallback_false(self):
+        @numba.jit
+        def fill_value(i):
+            return i
+
+        def inner_call_fallback():
+            x = 10
+            a = np.empty(shape=x, dtype=np.float32)
+
+            for i in numba.prange(x):
+                a[i] = fill_value(i)
+
+            return a
+
+        try:
+            numba_dppy.compiler.DEBUG = 1
+            numba_dppy.config.FALLBACK_ON_CPU  = 0
+            with captured_stderr() as msg_fallback_true:
+                with dpctl.device_context("opencl:gpu") as gpu_queue:
+                    dppy = numba.njit(parallel=True)(inner_call_fallback)
+                    dppy_fallback_false = dppy()
+
+        finally:
+            ref_result = inner_call_fallback()
+            numba_dppy.config.FALLBACK_ON_CPU  = 1
+            numba_dppy.compiler.DEBUG = 0
+
+            not np.testing.assert_array_equal(dppy_fallback_false, ref_result)
+            not self.assertTrue('Failed to lower parfor on DPPY-device' in msg_fallback_true.getvalue())
+
+
+if __name__ == '__main__':
+    unittest.main()